With growing concerns about global environmental issues and energy issues, solar batteries have been attracting attention as a clean, sustainable means of energy generation. When solar batteries are used in outdoor environment such as on the roof of a building, they are used to form a module.
A solar cell module is generally manufactured through the following procedure: First, crystalline solar cells containing for example poly- or mono-crystalline silicon (hereinafter referred to as “photovoltaic devices” or “cells” in some cases), or thin-film solar cells containing a thin film (several micrometers in thickness) of amorphous or crystalline silicon deposited on a glass or other substrate are provided. Next, in the case of a crystalline solar cell module, a module assembly is constructed in which a solar cell module protection sheet (front protection sheet), a solar cell encapsulant, the crystalline solar cells, a solar cell encapsulant, and a solar cell module protection sheet (rear protection sheet) are sequentially layered on top of each other. On the other hand, in the case of a thin-film solar cell module, a module assembly is constructed in which the thin-film solar cells, a solar cell encapsulant, and a solar cell module protection sheet (back protection sheet) are sequentially layered on top of each other. A solar cell module is then manufactured for example by a vacuum lamination process in which the module layers are laminated together under heat and pressure. Solar cell modules manufactured in this manner exhibit weather resistance, lending themselves to be suitably used in outdoor environment such as on the roof of a building.
For its superior flexibility, adhesion and other properties, ethylene-vinyl acetate (EVA) copolymer has been widely used as the material of solar cell encapsulants. For example, Patent Literature 1 discloses an encapsulant film which is formed of an EVA composition containing a crosslinking agent and a trimellitate and which exhibits superior adhesion and film-forming property. However, with regard to the use of EVA compositions as the constituent material of the solar cell encapsulants, there have been concerns about possible negative impacts on the solar cells by acetic acid gas and/or other components generated upon decomposition of EVA.
In an effort to solve the foregoing problem, it has been proposed to employ polyolefin materials as the encapsulant film materials, particularly ethylene materials from the perspective of their superior insulation property.